Computer is overheating and needs to be cleaned. Help?

Problems I know so far it it has:

1.) Needs new battery

2.) Has difficulty connecting to a network so might need a new modem - I think

3.) Having trouble disassembling

4.) Slow start up and runs slow

I have an old computer that my boyfriend wants me to clean out but I am not familiar with it. I am having trouble lifting up the front frame without accidentally harming something like a few connectors. Any suggestions? Or a link to a disassembly guide or video?

It is an older computer and I was going to check out to see if it is worth fixing up. Any help would be greatly appreciated because I have only found one video and a guide to clean the fan or place some easy parts. I want to remove everything to get the dust out. I think that is a huge cause of the overheating and it needs a battery replacement.